The Thomas Viaduct is a historic railway bridge located in Elkridge, Maryland. Completed in 1835, it is notable for being one of the oldest multiple-arch stone viaducts in the United States. The structure spans the Patapsco River and was designed to support the Baltimore and Ohio Railroad, facilitating transportation and commerce in the region. The viaduct features a series of seven arches, each measuring 40 feet in height. Its construction utilized local granite, showcasing the engineering skills of the time. The Thomas Viaduct remains an important landmark, recognized for its historical significance and engineering innovation.